Schematic
representation of the atomic force microscope interacting
with the material
surface in research on investigating phase changes
in nanoscale
materials. (Credit: Rama Vasudevan, ORNL)
(December 29, 2015) Understanding
where and how phase transitions occur is critical to developing new generations
of the materials used in high-performance batteries, sensors, energy-harvesting
devices, medical diagnostic equipment and other applications. But until now
there was no good way to study and simultaneously map these phenomena at the
relevant length scales.
Now, researchers at the Georgia Institute of Technology and
Oak Ridge National Laboratory (ORNL) have developed a new nondestructive
technique for investigating these material changes by examining the acoustic
response at the nanoscale. Information obtained from this technique – which
uses electrically-conductive atomic force microscope (AFM) probes – could guide
efforts to design materials with enhanced properties at small size scales.
The approach has been used in ferroelectric materials, but
could also have applications in ferroelastics, solid protonic acids and
materials known as relaxors. Sponsored by the National Science Foundation and
the Department of Energy’s Office of Science, the research was reported
December 15 in the journal Advanced Functional Materials.
“We have developed a new characterization technique that
allows us to study changes in the crystalline structure and changes in
materials behavior at substantially smaller length scales with a relatively
simple approach,” said Nazanin Bassiri-Gharb, an associate professor in Georgia
Tech’s Woodruff School of Mechanical Engineering. “Knowing where these phase
transitions happen and at which length scales can help us design
next-generation materials.”
In ferroelectric materials such as PZT (lead zirconate
titanate), phase transitions can occur at the boundaries between one crystal
type and another, under external stimuli. Properties such as the piezoelectric
and dielectric effects can be amplified at the boundaries, which are caused by
the multi-element “confused chemistry” of the materials. Determining when these
transitions occur can be done in bulk materials using various techniques, and
at the smallest scales using an electron microscope.